package utils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Base64编码工具类
 *
 * @author liufeng
 * @date 2012-10-11
 */
public class Base64 {
    private static final char [] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" .toCharArray();

    public static String encode( byte [] data) {
        int start = 0 ;
        int len = data.length;
        StringBuffer buf = new StringBuffer(data.length * 3 / 2 );

        int end = len - 3 ;
        int i = start;
        int n = 0 ;

        while (i <= end) {
            int d = (((( int ) data[i]) & 0x0ff ) << 16 ) | (((( int ) data[i + 1 ]) & 0x0ff ) << 8 ) | ((( int ) data[i + 2 ]) & 0x0ff );

            buf.append(legalChars[(d >> 18 ) & 63 ]);
            buf.append(legalChars[(d >> 12 ) & 63 ]);
            buf.append(legalChars[(d >> 6 ) & 63 ]);
            buf.append(legalChars[d & 63 ]);

            i += 3 ;

            if (n++ >= 14 ) {
                n = 0 ;
                buf.append( " " );
            }
        }

        if (i == start + len - 2 ) {
            int d = (((( int ) data[i]) & 0x0ff ) << 16 ) | (((( int ) data[i + 1 ]) & 255 ) << 8 );

            buf.append(legalChars[(d >> 18 ) & 63 ]);
            buf.append(legalChars[(d >> 12 ) & 63 ]);
            buf.append(legalChars[(d >> 6 ) & 63 ]);
            buf.append( "=" );
        } else if (i == start + len - 1 ) {
            int d = ((( int ) data[i]) & 0x0ff ) << 16 ;

            buf.append(legalChars[(d >> 18 ) & 63 ]);
            buf.append(legalChars[(d >> 12 ) & 63 ]);
            buf.append( "==" );
        }

        return buf.toString();
    }

    private static int decode( char c) {
        if (c >= 'A' && c <= 'Z' )
            return (( int ) c) - 65 ;
        else if (c >= 'a' && c <= 'z' )
            return (( int ) c) - 97 + 26 ;
        else if (c >= '0' && c <= '9' )
            return (( int ) c) - 48 + 26 + 26 ;
        else
            switch (c) {
                case '+' :
                    return 62 ;
                case '/' :
                    return 63 ;
                case '=' :
                    return 0 ;
                default :
                    throw new RuntimeException( "unexpected code: " + c);
            }
    }

    /**
     * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned.
     */

    public static byte [] decode(String s) {

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            decode(s, bos);
        } catch (IOException e) {
            throw new RuntimeException();
        }
        byte [] decodedBytes = bos.toByteArray();
        try {
            bos.close();
            bos = null ;
        } catch (IOException ex) {
            System.err.println( "Error while decoding BASE64: " + ex.toString());
        }
        return decodedBytes;
    }

    private static void decode(String s, OutputStream os) throws IOException {
        int i = 0 ;

        int len = s.length();

        while ( true ) {
            while (i < len && s.charAt(i) <= ' ' )
                i++;

            if (i == len)
                break ;

            int tri = (decode(s.charAt(i)) << 18 ) + (decode(s.charAt(i + 1 )) << 12 ) + (decode(s.charAt(i + 2 )) << 6 ) + (decode(s.charAt(i + 3 )));

            os.write((tri >> 16 ) & 255 );
            if (s.charAt(i + 2 ) == '=' )
                break ;
            os.write((tri >> 8 ) & 255 );
            if (s.charAt(i + 3 ) == '=' )
                break ;
            os.write(tri & 255 );

            i += 4 ;
        }
    }
}